Humidification has become a standard of care for Continuous Positive Airway Pressure (CPAP) therapy for sleep apnea, and for oxygen therapy, which is used for various lung disease treatment processes. Breathing normally, the air is warmed, filtered and humidified while going through a patient's nose before the air passes to the lower airways. The airway lumen is lined by epithelial cells with many hair-like cilia that transport mucus and foreign particles out of the lungs. The removal of moisture from the airways can cause the mucus to become dry and sticky, inhibiting the removal of particles. A study has shown that breathing dry air for only 30 minutes can cause the mucociliary transport to slow down due to water loss. (https://www.fphcare.co.nz/files/documents/hospital/therapy-overview-brochures/niv-humidification-therapy-review-niv_en_185042174/) Inadequate humidification may cause distress to CPAP and oxygen patients and may have serious consequences. These deficiencies can result in drying the oral and nasal airways, causing a sore, dry and inflamed throat and an increase in airway resistance and also result in increased rhinitis/rhinorrhea and nasal congestion. Thickened secretions reduce mucociliary clearance in extreme cases, resulting in the formation of a mass of secretions, which can occlude the airway. Increased bronchoconstriction further restricts the flow of gas to the lungs and increases the work of breathing (WOB).
Sleep apnea, if left untreated, increases the risk for a number of conditions, including high blood pressure, heart attack, stroke, obesity, diabetes, heart failure, arrhythmia, and work-related or driving accidents. CPAP includes the use of positive airway pressure applied through the nasal airway to alleviate obstructed breathing passageways during sleep.
A drawback with commercially available CPAP devices is that the flowing air tends to dry out the patient's nasal mucosa, thus reducing compliance. A number of solutions have been attempted. Passive humidification has been used, in which the high pressure air passes over cool water, but this increases humidity only by a small amount. Heated humidifiers have also been used, in which a heating pad is placed under a water tub, thus producing water vapor which may be picked up by the pressurized air stream. This increases relative humidity from the initial level of about 45-50% to an improved level of about 60-80%, and this has consequently improved CPAP compliance.
CPAP machines have become smaller and quieter over the years, but an undesirable byproduct of these advancements has been an increase in heat buildup, which manifests as rainout/condensation buildup in the non-heated tubing through which the pressurized air transits. Heated tubing has been implemented to increase the temperature of the outer diameter of the tube, to insulate the heated humidified air traveling through, thereby preventing condensation. However, although condensation is prevented, the relative humidity of the air stream is lower than with use of a heated humidifier as described above. The heated tube dries out the air, usually dropping the Relative Humidity by as much as 10-30%, contributing to patient discomfort and decreasing compliance with CPAP therapy. There are estimated more than 22 million CPAP users in the U.S. and more than 100 million worldwide, and even with the heated humidifier technology available today, it is estimated that 50% to 70% still complain of nasal and oral dryness.
There is a need for an improved method to humidify high pressure gas streams such as air or oxygen for use in therapeutic methods.